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J.M. Gabrielse Extension Lifts Rack & Pinion The rack is attached to one linear slide. The pinion (driven gear) is attached to the other slide The driven gear must be mounted where the linear slides always overlap. mount the motor bracket where the linear slides always overlap driven sprocket motor

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J.M. Gabrielse Scissor Lifts When the bottom of the scissors is pulled together it extends upwards. In this example a rack and pinion pulls the bottom of the scissors together. Scissor lifts work much better with small VEX robots than big FIRST robots. driven gear motor

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J.M. Gabrielse Scissor Lift Considerations Advantages –Minimum retracted height - can go under field barriers Disadvantages –Tends to be heavy to be stable enough –Doesn’t deal well with side loads –Must be built very precisely –Stability decreases as height increases –Loads very high to raise at beginning of travel motor

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J.M. Gabrielse The motor rotates the chain. The linear slide is attached to the chain. The linear slide is pulled up and down by the chain. Cable tie chain to the bottom of the linear slide. driven sprocket Extension Lifts Single Stage Chain Lift

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J.M. Gabrielse CanBot posted on www.vexforum.com by VexLABSwww.vexforum.com The motors are attached to the robot. The chain is zip-tied to the lift. The lift goes up and down with the chain. Single Stage Chain Lift

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J.M. Gabrielse Extension Lifts: Winches Winches are motorized spools. The motor pulls the string by winding it around the spool. The string is wrapped over a pulley so it pulls up on the linear slide. Gravity pulls the linear slide back down. Winding string or chain is very difficult. Friction and tangles often make these lifts unreliable. Attach the string (or chain) to the bottom of the linear slide. driven spool

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J.M. Gabrielse Winch posted on www.vexforum.comwww.vexforum.com by Stonebot A motor wraps string around a spool. The string is looped over the top of the tower so it pulls up on the extension. spool

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J.M. Gabrielse Extension Lift Considerations Best if powered up AND down –If not, make sure to add a device to take up the slack if it jams Segments need to move freely Need to be able to adjust chain/cable lengths. Minimize slop/ free-play Maximize segment overlap –20% minimum –more for bottom, less for top Stiffness is as important as strength Minimize weight, especially at the top

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J.M. Gabrielse Extension: Continuous Rigging Cable moves at the same speed for up and down Intermediate sections sometimes jam Low cable tension More complex cable routing The final stage moves up first and down last Slider (Stage3) Stage2 Stage1 Base

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J.M. Gabrielse Extension: Cascade Rigging Up-going and Down-going Cables Have Different Speeds Different Cable Speeds Can be Handled with Different Drum Diameters or Multiple Pulleys Intermediate Sections Don’t Jam Much More Tension on the lower stage cables –Needs lower gearing to deal with higher forces I do not prefer this one!